vSphere Support

[Diaphteiros]

What this PR does / why we need it:

This PR adds support for the vSphere infrastructure from VMware.

It is currently work in progress, there are still some open issues:

• fix missing loadbalancer class in dashboard
• documentation, documentation, documentation
• add possibility to configure default machine class for shooted seeds
• enable customization of seed backup bucket

Release note:

Added support for vSphere

It is now possible to configure a different blobstore for the seed backups or deactivate them completely. The backup for the virtual cluster etcd can also be deactivated now.

The `landscape.iaas[*].extensionConfig.machineImages` configuration for Openstack has been moved to `landscape.iaas[*].machineImageDefinitions`. Please adapt your acre.yaml accordingly.

`infoblox-dns` has been added as a DNS provider.

Upgrade Gardener dashboard to `1.46.1`

[Diaphteiros]

Update: missing loadbalancer class is a bug in dashboard. Already fixed, waiting for release: gardener/dashboard#787

[Diaphteiros]

Update: it is already possible to overwrite the default machine class used for shooted seeds, see worker config

[Diaphteiros]

Update: It's now possible to configure the seed backup blobstore. Also, I added some documentation. It could be better, but I'm lacking vSphere expertise to give a more detailed explanation.

[CLAassistant]

All committers have signed the CLA.